Incontinentia Pigmenti Type 2 (IP2) is a neurocutaneous genodermatosis showing X-linked dominant inheritance with prenatal male lethality. Affected females are diagnosed at or soon after birth by the presence of a progressive skin rash which is present in streaks or patches following lines of Blaschko. The rash is initially vesicular with marked eosinophilia, and becomes sequentially verrucous, hyperpigmented, and finally hypopigmented. Other findings include dental abnormalities, nail dystrophy, breast hypoplasia, patchy alopecia, and vascular abnormalities of the retina. The retinal abnormalities are the most significant complication of IP2, since they can lead to secondary retinal detachment, micropthalmia, and congenital cataracts. The disease has been mapped to distal X28. This application seeks to identify the gene for IP2, to determine its sequence and genomic organization, to characterize mutations in IP2 patients, and to define the function of the IP2 gene product. The IP2 critical region will be refined by characterization of additional recombination events. Yeast artificial chromosomes spanning the critical region will be used to identify cosmids, which will be assembled into contigs. These cosmids will be used to scan for genomic rearrangements in IP2 patients by Southern hybridization and by fluorescence in situ hybridization. Cell lines carrying the IP2 mutation on the active X chromosome will be isolated and used to identify differentially expressed mRNas. Any which map to the IP2 critical region will be pursued as candidates. Human homologs of the mouse xlr3 genes, which lie within the critical region for Striated, a mouse mutation which may represent the mouse homolog of IP2, will be identified and tested as candidates. Genomic sequence data will be analyzed as it becomes available. ESTs which are mapped by sequence identify, as well as putative exons identified by computer algorithms such as GRAIL, will be used to clone full-length cDNAs. These will then be tested as candidates. When the gene is identified, its complete sequence and genomic organization will be determined. The mutation present in each IP2 family will be determined, and will be related to phenotype and presence or absence of skewed X inactivation. The expression pattern of the gene will be studied by RNA in situ hybridization to mouse embryo sections. The subcellular localization of the IP2 protein product will be determined using monoclonal antibodies, and cell lines carrying IP2 mutations will be compared with normal cell lines. Other proteins which interact with the IP2 protein will be identified using the yeast two-hybrid system.